For a transmitter in a communication system, a DAC (digital to analog converter) with a filter is always required. For different communication systems, a DAC may operate at different sampling rates and the filter may need different corners. In a wide-band system, the DAC may operate at a high sampling rate. However, the high-speed interface for transmitting data to the DAC cannot be precisely predicted. Also, the speed of the interface may be limited due to the loading and the DAC cannot reach the high-speed sampling rate.